So, I had a 2012 MBP with an M500 SSD drive formatted APFS with High Sierra running fine. I removed the drive and put it in an external USB3.0 enclosure. I've found that this drive is not seen and won't boot by a 2010 13" MBP and a Late 2013 15" rMBP but WILL BE SEEN AND BOOT by an Early 2013 13" rMBP. I can't find any rhyme or reason for this. Any thoughts? Also, my intention was to install this drive in the 2010 MBP. But this computer doesn't see the APFS drive to boot whether installed internally or via the USB enclosure. On top of that, I've had trouble installing anything but Yosemite in the computer. El Cap, Sierra and High Sierra give me issues. The High Sierra USB installer for instance, won't even boot the computer. And I tried two different downloads of the installer on two different USB 3 sticks.